Various tension anchorage devices have been proposed which may be used, for example, to anchor supporting or guy lines for electric transmission towers. Some of these anchorage devices have utilized tension bars or tension wires embedded into drilled holes extending into the ground where the rods or wires are connected to large anchor blocks which are of greater diameter than the drilled holes. A problem with this type anchorage device is that it necessitates heavy, cumbersome drilling and digging equipment to drill and dig holes of sufficient size to provide the space for the enlarged anchorage blocks. Transmission towers are often erected in mountainous or hilly terrain and are guyed by supporting cables which may extend a considerable distance from the base of the towers with the result that the ends of the supporting cables are often anchored in relative hard-to-get-to areas. This requires that sufficient access routes or paths be made in order to transport the drilling and digging equipment to the area of the anchorage device. Such routes, particularly in hilly or mountainous regions, are expensive to make.
Other anchorage devices have utilized drilled holes which have extended a considerable distance into the ground depending upon the tension loads and soil conditions encountered. Where tension rods are utilized, such rods are of a length sufficient to contact the bottom of the drilled holes with the result that the rods are unwieldy to handle. If the rods are sectioned in shorter lengths, then they require relatively heavy coupling members to connect the rod sections together in order to withstand the tension loads.
In some instances pre-tensioned strand is placed in drilled holes after which grout is pumped into the holes. This requires tensioning equipment as well as an additional structure to hold the strand in tension while grout is injected into the hole. All this equipment must be brought to the anchorage area, which as explained above, may present a problem in hilly and mountainous terrain.
Anchorage devices also must be designed to withstand corrosion over a period of time. Devices have been proposed which involve pre-tensioning wires or rods positioned in tubes which are then filled with grout where the tube acts as protective covering for the wires or rods to prevent corrosion. The tube, including the grouted wires or rods, is then inserted into a pre-drilled hole after which additional grout is inserted between the tube and the sides of the pre-drilled hole. The insertion of the wires or rods into the tube usually is done at a workshop remote from the anchorage area thus making it difficult to transport the tube, grout, wire or rod assembly to the anchorage area.
A further difficulty arising from using rods as tension members, particularly in long pre-drilled holes, is that the hole must be drilled in a straight line to accommodate the straight rod. This is also difficult unless heavy rugged drilling equipment is utilized, which as explained above, may be difficult to position in rough terrain.
It is therefore an object of our invention to provide for an anchorage device which may be conveniently assembled at an anchorage site utilizing conventional drilling equipment without requiring use of any digging equipment to make large holes in the ground. It is a further object of the invention to provide for an anchorage device which will be projected against corrosion and which at the same time may be made from conventional materials readily available on the market.
It is a further object of our invention to provide for an anchorage device which will accommodate slight irregularities in the direction of a drilled hole in the ground while at the same time provide intimate contact between the member of the device adapted to withstand tension forces and grout which surrounds the tension member. The tension forces in the tension member are then transferred by shear forces in the grout to the sides of the drilled hole to hold the tension member in place.